Evaluation of fertilizer additions to stimulate oil biodegradation in sand seashore mesocosms

Abstract

Effects of fertilizer additions for oil degradation were examined in sand seashore mesocosms. Within 37 days, up to 85% removal was achieved by the addition of slow-release type fertilizer (SRF) with the initial degradation rate of 423.3 mg oil (kg sand)(-1) day(-1). The removal was mostly of biological origin based on the changes of C(17)/pristane and C(18)/phytane ratios from 2.60 to 0.81 and from 3.55 to 1.29, respectively. The addition of oleophilic fertilizer (Inipol EAP22) was less effective and resulted in the removal of 64% of the added oil (3%, v/v) with a lower initial degradation rate. Petroleum-degrading bacteria had achieved a value of 1 x 10(8) CFU (g sand)(-1) at Day 3 and this peak exactly coincided with the initial degradation in the SRF-treated mesocosm. In this mesocosm, surface tension values were decreased drastically during Days 3 and 8, suggesting that microbially-produced surface-active agents actively enhanced the oil degradation rate and cell proliferation. Although the Inipol-treated mesocosm appeared to show significantly enhanced oil degradation compared to that of the untreated control mesocosm, Inipol was found to be less effective than SRF in enhancing a true oil-degrader when compared under similar experimental conditions.